Chromatin fractions isolated by ion-exchange chromatography on ECTHAM-cellulose have been shown to differ in composition, structure and in vitro transcribability. Complementary DNA's have been prepared to rabbit globin mRNA and to the polysomal polyadenylate containing RNA of rabbit liver. Hybridization will be used to study the interaction of these cDNA's with DNA from ECTHAM-cellulose fractions using rabbit liver as chromatin source. This will provide both active genes and inactive genes for localization in the fractionated chromatin. The elution position of nucleolar chromatin and the localization of ribosomal genes will be investigated. The localization of chromatin binding sites for control elements, e.g., steroid receptor complexes, will be studied. The types of RNA associated with the chromatin fractions will be evaluated through hybridization with either RNA or DNA complementary to messenger and ribosomal RNA.